Dichroscope

by Ritika Changrani

Dichroscope is a tool used to differentiate similar looking gemstones based on the dichroic property of the gemstones.

Some gemstones are singly refractive. They exhibit only one colour to observer. There are also gemstones which exhibit two different colours of light. But most of that is not detected by the human eye since the two colours produced are so close in wavelength that it becomes difficult for the human eye to identify them. The two colours in such gemstones mix up to give a slightly different colour. Such stones are called doubly refractive gemstones. For example, ruby is made up of dark red and light pink colour. But it appears to the viewer as light red.

The property of the gemstone to exhibit two different colours or shades when turned in two different directions under light is called as dichroism. Examples of the gemstones which are Dichroic are sapphire, zircon, tourmaline and topaz.

Dichroscope is a tool used to differentiate similar looking gemstones based on the Dichroic property of the gemstones. Hence it can easily differentiate gemstones like ruby from tourmaline since ruby is Dichroic and tourmaline is pleochroic. Dichroscope also helps to determine Pleochroism and trichorism. Dichroscope helps to determine the optical properties of a gemstone. (image courtesy: www.faceters.com)

Dichroscope is a metal tube which is open on one end and has a lens at the other. It has an optical calcite mounted inside the tube and produces a double image of the square opening. Enough bright light is directed on a gemstone and viewed through the dichroscope. Dichroscope separates the different colours of light into its constituent colours. Light entering the dichroscope is broken into two polarized rays. Two images of different colours indicate that the vibrations are of different wavelengths and at right angles to each other. If dichroism is not detected in the first test, the gemstone has to be turned and output colours must be viewed in other directions too.

Pleochroism can be detected by rotating the instrument at an angle of 90 degrees. If the two colours switch sides on the split image, the gemstone is pleochroic. To determine trichorism, it is necessary to change the orientation of the stone. If one new colour is determined along with one of the colours of previous orientation, the gemstone exhibits trichorism. Trichroic gems show three different colours when viewed in three directions perpendicular to each other. Singly refractive stones produce only one colour on the dichroscope.

How does a Dichroscope work?

Dichroscope works on the principle of plane polarized light. Plane polarized light is the light of a specific wavelength that is separated from ordinary light and travels in a specific direction. Some waves may travel up and down and some side to side. When light traveling in different direction is being separated, it is possible to view the individual colours of specific wavelength.

Types of Dichroscopes

There are two different types of dichroscopes. They are London dichroscope and Calcite dichroscope.

London dichroscope

In a London dichroscope, two pieces of Polaroid orientated at right angles to each other are placed such that the light entering each polarizing filter are at right angles to each other. The two polaroids in a London dichroscope are joined together in same plane. London dichroscopes are much cheaper when compared to the calcite dichroscope but does not give as clear a result as the other. It is difficult to determine gemstones with weak Pleochroism with a London dichroscope.

Calcite Dichroscope

The calcite dichroscope is made up of a calcite crystal. The calcite has a special characteristic called bi-refringent. This property of calcite enables the gemstone to appear doubled when looking through it. The calcite crystal splits the light entering the dichroscope into two rays and thereby helps identify the difference in colours. The two rays form two images at right angles to each other.

Out of the two dichroscopes, the calcite dichroscope is the most commonly used in the gem testing laboratories to test the Dichroic property of the gem stones.

How to use a Dichroscope?

Hold the upper portion of the dichroscope near the eye – may be an inch from your eye. Place the gemstone near the opening. The other end of the dichroscope is hexagonal and hence it is easier to turn the dichroscope while testing. View the gemstone through the gem view opening. Slowly rotate the dichroscope to complete one full rotation and observe the colour difference of the two small squares which appear inside the dichroscope while you rotate. If you observe two colours while you rotate, the gemstone is dichroic. If three colours are observed, the stone is trichroic. Repeat the observation to confirm the number of colours observed. Observe the strength of the colours as it helps determine the type of gemstone. Always make sure that sufficient bright light is focused on the gemstone while you observe the colours using dichroscope. Never use fluorescent light since it can give a false result.

Advantages

• Dichroscope helps determine the pleochroic property of the gemstone which helps to separate different types of gemstones.
• It also helps to determine whether the gemstone exhibits weak Pleochroism or strong Pleochroism.
• Dichroscope also helps identify some gemstones.
• It also helps to study the optical properties of the gemstone

Polariscope

by Ritika Changrani

Polariscope is an instrument used in gemmology which helps to find if the gemstone is single refractive or double refractive and also allows determining the various crystal axis of the stone.

A Polariscope is used to determine whether the gemstone is natural or synthetic. This is one of the most commonly used instruments by the gemmologists. The use of plane polarized light allows us to see the actual path the beams are taking through the stone.

A polariscope is made of two Polaroid plates that rotate, a power switch, a stone holder and a bottom light source. Two polarized filters or plates are made of polarizing plastic sheets, one is on the top of the instrument, known as analyzer and the other is on the bottom of the instrument, known as polarizer. Polarizer and analyzer have their own vibrational planes. When the vibrational plane of polarizer and the vibrational direction of the analyzer are at right angles to each other, the field between them appears dark. This position is known as crossed position and it is in this position that the gemstones are tested to see if they are isotropic, anisotropic, anomalously double refractive and anisotropic aggregate. The polariscope can be used to determine the optical character as well as the optical sign of the gemstone.

Polariscope can also be used to determine the strains in diamond. It helps in separating natural gemstones from synthetic ones and also helps to distinguish solid inclusions from negative inclusions. Polariscope can also be used for recognizing polysynthetic twinning.

How to use a Polariscope?

• The polariscope is adjusted for cross position by setting the vibrational plane of polarizer and the vibrational direction of analyzer at right angles to each other.
• Turn on the light source and place the gemstone on the rotating platform above the polarizer. The gemstone is rotated in a vertical axis.
• Observe the gemstone through the analyzer and note down the observations
• Based on the observations the nature of the gemstone can be determined as follows.
  • If the stone remains dark throughout the 360 degree rotation, the stone is said to be isotropic or singly refractive.
  • If the stone darkens evenly at every 90 degree interval, the stone is said to be doubly refractive or anisotropic.
  • If the stone appears light throughout the rotation, it is said to be microcrystalline or crypto crystalline aggregate.
  • If the stone shows anomalous double refraction, the stone is singly refractive. Anomalous double refraction may be confusing at times. Hence when there is a suspicion that about anomalous double refraction, it is recommended to orientate the stone in the position where it appears lightest. Then turn the analyzer to 90 degree. If the stone appears lighter than before it is said to exhibit anomalous double refraction and hence is singly refractive. If the stone appears the same, it is doubly refractive.

How does a Polariscope work?

Polariscope works on the principle of plane polarized light. Single refractive gemstones do not break the plane polarized light into various colours. There is only one beam of light coming out. Examples of singly refractive gemstones include diamonds. Double refractive gemstones break the plane polarized light into two paths. One is the ordinary beam and the other is the extraordinary beam. Based on analyzing the transmitted light, the nature of gemstone can be identified. Some of the doubly refractive gemstones are quartz, tourmaline, ruby, zircon, peridot, sapphire and rulite.

Both the filters i.e. polarizer and the analyzer are turned to the dark position. When plane polarized light is passed through the gemstone, the singly refractive stone remains dark since it does not change the path of light. Hence it remains dark when observed in all positions. But in case of double refractive gemstone, when plane polarized light is passed through it, the stone changes the path of the light and hence the direction of the light wave changes. This produces light that is no more polarized. The change in direction of light makes the stone change from light to dark as it is rotated between the Polaroid plates.

Since the polariscope works through plane polarized light, it can be used to test transparent as well as translucent gemstones, but cannot be used to test opaque materials. Once the stone is found to be doubly refractive, a conoscope can help to determine the optic interference figure. Optic interference figure helps to locate the various directions in which the light is traveling through the stone. This information in turn helps to identify the type of gemstone. The different shadow patterns observed through the polariscope helps to determine the crystal structure and diagnostic patterns of the gemstone.

Types of Polariscope

There are two types of polariscope i.e. plane polariscope and circular polariscope. Circular polariscope work on circular polarized light unlike plane polariscope which works on plane polarized light. In a circular polariscope, two quarter wave plates are added to plane polariscope. One quarter wave plate is placed between the polarizer and the gemstone to be tested and the second quarter wave plate is placed between the analyzer and the gemstone. The quarter wave plates produce circularly polarized light. The advantage of using circular polariscope is that it helps distinguish isochromatics and isoclinics. But plane polariscope are more extensively used for testing gemstones.

Refractometer

by Ritika Changrani

A Refractometer is a gemmological tool used to find the ability of gemstone to bend or refract light. This measure is the refractive index of a gemstone.

A Refractometer can be used to measure the refractive index of both singly refractive (isotropic) and doubly refractive (anisotropic) gems. The refractive index helps to determine the composition and physical properties of gemstone. With the help of refractive index, it is easy to identify the type of gemstone. Also, it is possible to estimate the amount of impurity present in the gemstone by comparing the measured refractive index with the standard value of the natural gemstone. With the help of Refractometer, birefringence and optic sign of the gem can also be determined.

How does a Refractometer work?

Refractometer works on the principle of Total Internal Reflection i.e. when light travels from denser material or the material with higher refractive index to rarer material or the material with lower refractive index, the light reflects into the denser material or refracts into the rarer material depending on the angle of incidence of the light traveling. (image courtesy: www.diamondtech.com).

Refractometer is made of a metal case, polarizing filter on the top, glass hemicylinder and viewing lens at the bottom. Natural or white light is passed through the back of the unit. The light travels through the glass hemi cylinder and then to the gemstone which is placed on the glass hemicylinder using a special refractive index liquid, which seals the gemstone to the hemicylinder thereby removing the air in between them. This is done to maintain the same speed of light in both the glass hemicylinder as well as stone so that the refracted rays obtained are accurate. The light is then refracted and sent to the viewing lens through the glass hemicylinder. Through the viewing lens one can see the refracted rays of light. The bending or slowing of light caused by the gemstone appears as the light and dark area combined by thin green line. The green line thus obtained is the refractive index of the gemstone.

A Refractometer is designed such that the incident and exiting rays reach the boundary of hemicylinder at 90 degree. No refraction occurs when the light ray is at 90 degrees to the boundary. Therefore no refracted rays are visible and hence appear as dark areas on the scale. The reflected rays of light appear as the light areas on the scale of the Refractometer. The light and the dark boundary on the scale is the representation of critical angle.

How to use a Refractometer?

• Apply a small amount of refractive index liquid on the metal base near the hemicylinder. Slowly place the gemstone on the refractive index liquid. Then slide the stone to the centre of the hemicylinder. Take care that you don’t apply pressure on the stone as it may damage the hemicylinder. The liquid builds optical contact between the stone and the hemicylinder.
• Close the lid of the Refractometer to avoid external light.
• Place the light source at the back of the Refractometer. Adjust the beam until you see bright light when you observe through the viewing lens.
• Position your eye such that you can see the whole scale through the viewing lens without moving your eye. This is to avoid the parallax error in the reading.
• Move your head up and down until you can see the clear separation of light and dark areas. Note down the reading on the scale where the thin greenish line appears.
• Unscrew the polarizing filter and place it on the viewing lens.
• Take down the reading. Rotate the polarizing filter to 90 degree and note the readings.
• Polarizing filter helps to determine if the stone is singly refractive or doubly refractive. If the stone is singly refractive, only one shadow edge is seen. Note down the readings rotating the stone 135 degrees.
• If the stone is doubly refractive, shadow edges move between two values on the scale. Note down the two values, i.e. the upper and the lower value. Take down four sets of reading by rotating the stone to 45 degrees.
• If one of the reading i.e. either upper reading or the lower reading remains same, the stone is said to be uni-axial. If both the readings change after rotating the stone, the stone is said to be bi-axial.
• The refractive index is the difference between the largest higher reading and the smallest lower reading.
• f the difference is positive, the optic sign of the stone is positive; else the optic sign of the stone is negative.

Tips to Remember while using a Refractometer

• Store the equipment in a dry place to protect the device from moisture which can affect the accuracy of the equipment.
• While you move the gem stone on the glass hemicylinder, take care to move the stone slowly so that no scratch is caused on the hemicylinder. A minute scratch causes can damage it and turns costly to be repaired.
• The refractive index liquid has to be stored and sealed. Avoid its contact with hands or eyes.
• Make sure to use the tiniest drop of refractive index liquid since the liquid itself has its own refractive index and causes total internal reflection between hemicylinder and the liquid. This will in turn affect the accuracy of the reading.
• The contact liquid should be selected with proper care since it sets the limit to the stones tested. The stones with greater refractive index than the contact liquid cannot be tested and hence give negative reading.
• Make sure there is adequate amount of light. White light can be used while testing, but monochromatic yellow light is widely used. White light can give good results for single refractive stones, but for doubly refractive gems sodium light source is the best option. White light, when used with doubly refractive gemstones causes overlap of the refraction readings thereby getting wrong results. Also, the use of sodium light source clearly differentiates the boundary between dark and light areas and hence helps take the readings easily.

Spectroscope

by Ritika Changrani

A Spectroscope helps to identify cut stones, rough stones, mounted stones and unmounted stones to see whether they are real or fakes.

A Spectroscope is a gemological device used to test if the gemstone is natural or synthetic. Spectroscope helps to determine what parts of white light are being absorbed by the gemstone.

White light is made up of seven different colours namely violet, indigo, blue, green, yellow, orange and red, which have different wavelengths and travel with different speed. When white light is passed through a gemstone, a part of it, based on the energy level is absorbed by the gemstone and the remaining colours combine to give a different colour to the stone. When observed through the spectroscope, one can see bands or colours missing. The missing bands are the colours absorbed by the gemstone. The colours absorbed let us know the elements present and the chemical composition in the gemstone which thereby helps in gemstone identification.

Types of Spectroscope

There are two types of spectroscope, diffraction grating spectroscope and prism spectroscope.

Diffraction Grating Spectroscope

Diffraction grating spectroscope implies the principle of diffraction. Diffraction refers to the bending of light waves around a sharp edge or an obstacle by transmission or by reflection. This type of spectroscope is made up of high-dispersion diffraction grating film, movable slits and a photo detector which is used to measure the properties of light within the specified portion of the spectrum. Here light is made to enter a narrow slit. The light is then diffracted by thin high-dispersion diffraction grating film. This causes uniform spectrum image and disperses light into large visible spectrum. The advantage of diffraction grating spectroscope over the prism spectroscopes is that the spectrum is evenly distributed and hence is easier to read. But the spectrum thus produced is not as bright as that produced by prism spectroscope. Diffraction grating spectroscopes do not have an inbuilt calibration scale.

Prism Spectroscope

Prism spectroscope works on the principle of dispersion. Dispersion is defined as the splitting of white light into its constituent colours. Prism spectroscope is made of three optical grade glass prisms placed in optical contact with each other. Most of the prism spectroscopes come with calibration scale. But experienced people make observations without the scale.

In a prism spectroscope, light is made to enter through a narrow slit which is dispersed by passing through a series of prisms. In prism spectroscopes, the spectrum obtained is brighter and faint lines are clearly visible. But the disadvantage with prism spectroscope is that the spectrum is not evenly distributed. Blue parts are more spread and red parts are more condensed. It is difficult to distinguish lines in red part since they are very close to each other. Prism spectroscopes come with focus slide control and light slit control which allows adjusting for the amount of light entering the unit.

How to use a Spectroscope?

• First of all, before testing for the absorption spectra of the gemstones, hold the spectroscope against some different sources of illumination. Holding it against either a fluorescent light bulb or a computer monitor shows clear absorption bands.
• Place the gemstone on a black non-reflective surface may be a piece of black velvety cloth. If the surface is non-reflective, the observations may not be accurate and hence give false readings.
• Place the source of white light such that light enters the pavilion of gemstone at an angle of 45 degrees.
• Place the spectroscope on the other side at the same angle. The angle of 45 degree is chosen since this is the path in which light travels in the longest path picking up most colours.
• The other way of positioning can be by placing the light source and the gemstone in one line such that the light illuminates the gemstone from the back. This helps to view the gemstone in transmitted light.
• Note the observations through the spectroscope. Note down the spectrum seen with red end of the spectrum on the left and violet end of the spectrum to the right. The colours which are absorbed by the gemstone appear as missing bands. The colours absorbed mix up to give the gemstone a different colour.
• Based on the spectrum obtained, you can analyze the composition of the gemstone and hence determine the type of gemstone.
• The spectrum can also be compared with that of a known gemstone to identify if the gemstone is a natural or a synthetic one.

Though spectroscope is one of the important tools in gemology, it should be purchased only when it is extremely necessary. The cost of spectroscope is quite high. Furthermore, only experienced gemmologists can make use of the spectroscope more efficiently. It is difficult for an inexperienced person to study the nature of gemstones using a spectroscope.

Aquamarine Identification

by Erum Qureshi

Aquamarines, belonging to the Beryl family, are relatively easy to identify. Various simple tests can reveal the authenticity of an aquamarine stone.

Summary: Aquamarines, belonging to the Beryl family, are relatively easy to identify. Various simple tests can reveal the authenticity of an aquamarine stone.

Aquamarine – This name is derived from a Latin word, which means water of the sea and so named because of its seawater color.

Most gems have a bluish green color, which was highly prized at one time but has lost its charm lately. There are also clear green Beryls, which are colored by iron instead of the chromium colored emeralds and have a light, clear color, quite unlike the deep green of emerald. The other is the colorless variety, which is named Goshenite (after Goshen County in Hampshire County, Massachusetts). This name, however, is fast becoming redundant, and the name colorless beryl or white beryl is commonly used.

Species

Aquamarine belongs to the species beryl. Beryl is a silicate mineral having chemical formula Be3Al2 (SiO3) 6. Beryl of non-gem quality is mined as the raw material for beryllium, which is now increasingly used in industry. Aquamarine crystals are hexagonal and further, many of them exhibit a tapering form due to erosion.

Hardness

The hardness of aquamarine is 7.5 on the Moh’s scale. Like all Beryls, an aquamarine has a weak basal cleavage and a tendency to brittleness.

Determination of Specific Gravity (SG)

The SG of aquamarine lies between the range of 2.66 and 2.80. Some Madagascan stones have higher densities owing to a trace of alkali metal in their composition. The specific gravity or SG is measured by immersing the stone serially in a set of high-density liquids.

These liquids come in a set of three or five liquids of varying densities. They work on the simple premise that if a stone of lesser density is immersed it will float, that of higher density shall sink and one of equal density will remain suspended.

Refractive Index

The refractive indices for aquamarine vary from 1.572 to 1.590 for ordinary ray and 1.567 to 1.583 for the extraordinary ray.

The refractive index or RI is measured by placing the stone face down with a drop of contact liquid between the polished face of the gem and the glass of the Refractometer. The light rays leaving one medium (air) and entering another obliquely (the stone) will seem to bend a little at the place of contact. This is called refraction of light and the reading is taken herewith.

Pleochroism

Aquamarines exhibit a distinct Dichroism that is the ‘twin colors’, the strength of which depends on the depth of color of the stone – they are deep blue and colorless, the extraordinary ray giving the attractive blue color. The birefringence (difference between the highest and lowest refractive indices) is negative in sign and 0.005 for the lower indices and rises to 0.007 to 0.008 for the stones with higher indices.

Absorption Spectra

When the aquamarine is viewed through a spectroscope, the absorption spectrum it shows (ascribed to iron and not very pronounced) there is a broad band in the violet at 427 nm and a feeble diffuse band in the blue-violet at 456nm. Further, the extraordinary ray, which can be isolated by the use of a Polaroid disc, shows these bands more strongly, and in such conditions a narrow and delicate absorption in the middle green can be observed at 537nm.

Fluorescence

Aquamarine does not exhibit luminescence. All colorless Beryls, like the blue and sea-green stones show a strong greenish-blue color when viewed through the Chelsea filter. In this way, aquamarines can be picked out from a parcel of similar looking stones.

Treatment and look-alikes

Practically all the beautiful blue aquamarines seen in jewelry are greenish-yellow (or even brownish-yellow) stones, which have been heat-treated. The blue color is induced by heating to a temperature between 250 and 720 degree Celsius for a varying period. The resulting color is permanent.

The most effective imitation of the aquamarine is the synthetic spinel colored pale blue by cobalt. These synthetics will have a totally different refractive index (1.782) and SG (3.63) from aquamarine. Gemologists identify these synthetics by placing the suspected stone close to a strong light and viewing it through a Chelsea Filter held close to the eye. The synthetic spinel shows a distinct red under the filter, whereas aquamarine shows a decided green.

Jewellers Loupe

by Ritika Changrani

A jeweller’s loupe is a tool that helps identify the internal flaws, cracks and blemishes on the surface and any other cover ups on the gemstone.

A Loupe is just a magnifying glass. It helps to see the magnified image of gemstone and serves as the identification and grading tool. A Loupe is made of a powerful convex lens. Through a jeweller’s loupe, one can easily see the internal flaws, cracks and blemishes on the surface and any other cover ups on the gemstone. Jeweller’s loupe is the most important test equipment for testing gemstones.

How to Choose a Jeweller’s Loupe?

There are two important factors to be considered while choosing the right jeweller’s loupe. They are the size and magnification of the lens and the optical quality. Loupes are available in different sizes and powers. The standard size used for testing gemstones is of 18mm length with 10X, which magnifies the gemstone to ten times its size. The jeweller’s loupe is available in 20X and 30X, but they are not much used.

The jeweller’s loupe has to be tested for achromatic and spherical aberrations. Chromatic aberration refers to colour fringes of the image due to dispersion caused inside the glass lens. The loupes which are corrected from chromatic aberration are known as achromatic. Spherical aberration refers to the distortion caused due to the differences in refraction on the outer edges of the lens and the rays traveling through the center. The loupes which are corrected for spherical aberration are termed as ‘aplanatic’.

While choosing a jeweller’s loupe it is necessary to check that they are achromatic and aplanatic to get accurate results. In a better quality jeweller’s loupe, three lenses (known as triplet loupe) are used so that the field of vision is in focus to the edges and no false colour is imparted to the eye. The use of three lenses eliminates the pin cushion distortions and chromatic and spherical aberrations.

While selecting a jeweller’s loupe you can easily identify if they are achromatic and aplanatic. Look at the white light through the loupe. If the white light remains white without changing the colour, the lens is corrected for chromatic aberration. Similarly spherical aberration can be tested by looking at the mm squared drawing paper. If they remain squares when looking through the loupe, the loupe is aplanatic.

It is also better to choose a loupe with black framing around the lens, since this avoids reflections which may alter the color of the object under view. Do not opt for golden or other bright coloured frames since they interfere with the colours.

How Does a Jeweller’s Loupe Work?

Jeweller’s Loupe magnifies the image of the stone under test as per its magnification power. Suppose, we are using a 10x loupe, the image is magnified to ten times its original size. This helps us clearly see the flaws, cracks and other distortions in the stone. A triplet loupe consists of one ‘plano-convex lens’, one bi-concave lens and one bi-convex lens. The ‘plano-convex lens‘ is used to eliminate spherical aberration and the other two are used to eliminate chromatic aberration. Depending on the observations, the nature of the gemstone can be detected. Jeweller’s loupe helps to detect diamonds, sapphire, alexandrite, ruby, pearls and many other gems.

How to Use a Jeweller’s Loupe

• Remove your spectacles if you are wearing one. Unfold the jeweller’s loupe.
• Hold the jeweller’s loupe between the thumb and the index finger. Keep the jeweller’s loupe as close to the eye as possible without touching the eyeball. The loupe should be so close that your eyelashes almost brush through it. Once the loupe is close to your eye, see that it is kept stationary by letting the back of the thumb rest against the side of the nose. Keep the remaining three fingers in parallel or just below the index finger. Keep both your eyes open to avoid eye straining.
• Make sure there’s enough light in the place where you are observing the gemstone. Fluorescent and other light bulbs lack some colours which are necessary. Hence sunlight is the best light for the testing gemstone. Diamond lamps can also be used.
• Place a clean white soft cloth on the surface you are using. This helps to avoid scratches on the gemstone and also avoids rolling down in case it slips down. Next, place the stone at a distance of an inch or a little more on the other side of the gem loupe. Peering through the gem loupe, move the stone to and fro until it comes in focus. Keep moving the stone front and back and turn the stone in different directions until the area of the stone is seen with sharp focus.
• Note the external and internal features of gemstones. Look if there is unevenness in colour. If there is unevenness in colour, there is a possibility that the gemstone is dyed or painted to imitate a high quality gem. Many deceptions which cannot appear to the naked eye can be observed through the jeweller’s loupe. If you already have some real gems of similar types, you can observe both and compare them.
• Some of the things you should observe while testing the gemstone through the loupe are :
  • Symmetry: Check if the gemstone has a balanced symmetry
  • Number of facets: Observe whether the gemstone has the right number of facets required for the particular cut
  • Sharpness of the facet edges: Hard stones have sharp edges while synthetic stones have soft edges
  • Inclusions, flaws and bubbles in gemstones: Inclusions, if present, don’t necessarily indicate that the gemstone is bad. Instead, the gemstone can be a natural gem. Flaws in gemstones are not an indication that the gemstone is of low value. Bubbles in gemstone indicate that the gemstone is synthetic.
  • Scratches and cracks in gemstone: Soft stones tend to scratch easily while hard stones crack.

Gemstone Mining Methods

by Sheweta Dhanuka

Gemstones are treasured by most of us and to retrieve these precious gems from deep down the earth crust one has to go in for treasure hunt. Gemstone Mining is very complex and tedious process that requires huge input of valuable resources such as time, workforce, equipments and knowledge etc. There are different methods for recovering the gemstone from the lap of Mother Nature. The appropriate procedure is selected depending upon the circumstances but no matter what method is selected the entire process of gemstone mining needs to be very systematic as it costs a lot of money. The total process of gemstone mining is so intricate that inspite of putting in so much efforts there is no surety of the results. Failures and disappointments always have higher percentage than the success.

In order to attain the positive results, the first and foremost requirement of this exclusive process is to identify the gemstone deposits. This necessitates the vast knowledge of gemstone properties, with the help of this key the deposits are identified where there could be the probability of the finding the precious and semi precious gems. The route of gemstone mining is executed all the way through highly developed and technical system. But we all know, traditional methods have there own uniqueness that cannot be denied even after developing new scientific methods. All the methods are categorized into two types of mining viz. surface mining and underground mining. First always the surface mining is done and then when fruitful results are not achieved underground mining is brought into action. Underground mining is always more expensive because –

• It takes long working hours.
• For underground mining more advanced equipments are required.
• There are extra costs incurred for activities such as pumping, electricity, digging etc.

Surface Mining

Surface Mining is done to obtain gemstones from the rocks near to the surface of the land. There are six different types in which surface mining could be done. The miner decides on surface mining technique depending up the overall cost and time. These methods are:

[1] Hydraulic Mining

In this method powerful jets of water is used to loosen the gem material from the overburden. The miners make channels on the rock/gravel hillsides in form of sluices where water under pressure is sprayed. The water pressure splits down the rock and washes large rock piece of it downhill. And finally the gems as raw stones are separated. This mining is very harmful for the environment as it wrecks the mountains and blocks the rivers. Hydraulic surface mining was found way back in 1800s and continued till 1960s but now it is stopped completely due to its disastrous consequences to the natural beauty.

[2] River Panning

River Panning is the method where gemstones are collected while washing the gravels from a river/stream in the mining area. It is also known as placer mining. This method is initiated with the identification of the gravel which may contain gems. The best place to find the gravel deposits is in obvious gemstone producing rivers, streams and creeks. Then a large pan is filled with water and shaking it back and forth to settle the heavy material to the bottom of the pan. The lighter material is washed over the top of the pan and larger rocks & pebbles are removed by scooping them over the edge. These steps are repeated until there is only about a tablespoon or two of concentrates left in the pan. Nearly all panning is completed using the riffles in the pan.

The left over concentrated is then shifted to a smaller clean pan. Drop of liquid soap is added to keep the tiny chips from “floating.” The less weighty material shall float down with the water and the gems, in case the gems are there, it shall stick and stay at the upper end of the pan. This is a very time consuming method and the chances of success are very less.

[3] Open Pit Mining

This mining can only be accomplished under the guidance of an experienced Gemologist. First he scrutinizes the location to be mined with respect to value of the rock and minerals below the surface, cost of digging the mine and the after effects of mining on the environment. The monetary value of rocks and minerals keeps appreciating over the years so once it is profitable to mine then only open pit mining is done.

Once the location is finalized, layers of the land are removed one after the other till rocks are visible. Then the rocks are removed and gems are searched for in the rocks and sent for further processing. Sometimes explosives like dynamite are used to reach deeper and deeper to recover the required rock possessing the gems. After the mining is done, the area turns into pit which is used as landfill. Landfill is huge open space used for dumping the garbage. Once it is fill it is covered the layer of mud. Finally when the trash decomposes in long run and land can be again used for some other purpose apart from mining. This mining method is relatively easy and cost effective. However, it is performed only when rocks are near to the surface of the land.

[4] Strip Mining

This process is very similar to open pit mining. The mining site is identified; the trees and bushes are removed with the help of the bulldozer. The remains are dumped at the nearby area. Many small-small holes are drilled distant from one another through the rock. Dynamite are placed inside these holes and blasted to get the rocks with gemstones. Raw stones then are sent for further processing. This mining is done in long strips so it is called as strip mining. Once the first strip is completed, the second strip starts. The dirt obtained in making the second strip is dumped in the first strip. Similarly it goes on till the entire site is worked on. And in the last strip the remains of the first strip is filled in. The top layer is of mud that is leveled on all the strips together making the land ready of re-use.

[5] Mountaintop Removal Mining

In this mining method, the mountain top at the ground level is cleaned by cutting the trees and shrubs. Then using the dynamite the top of the mountain is blasted for making the vein. This gives huge blocks of rocks from which the gemstone in unprocessed form are retrieved. The dirt obtained after the blast is dumped into the valleys with the help of bull dozers and trucks.

[6] Quarrying

This mining method is quite less hazardous to the environment. The rock attained from this mining is used for making buildings. Therefore, the way quarrying is to be done depends upon the purpose of re-use of rock. The rocks are drilled to use the left over for cement, it is blasted with dynamite to use the rocks for the interiors of the house like flooring, kitchen slabs. In any of the method after getting the rock the gemstones are searched and then the rocks are spared for re-use.

Underground Mining

Underground mining is done when surface mining is not possible or does not yield rewarding results. Moreover, precious gemstones are mostly found through underground mining. In the method the miners make underground rooms where they further dig the ground more and deeper. Underground mining is done in numerous ways. These are –

[1] Borehole Mining

As the name suggests holes are drilled very deep inside the plain land. In these holes a long huge tube (having enough space to allow the water to pass through) is dropped. Then water is pushed down the tubes with the force, the water hits the rock and breaks it down. The water combines with the rocks, dirt and mud to make slurry. This mixture is pumped back from the tubes and stored into tanks. The unwanted water is thrown out the left over rocks are processed for gems. This method is very much environment friendly and the shifting from one place to another is quite easy.

[2] Drift Mining

This mining is done on the mountain sides. Rock are identified which are on the sides of the mountain. The opening is made below the identified rock. These opening are made horizontally and are known as tunnels/drifts. From the drifts the desired materials are retrieved as due to gravity the material comes down the hill easily. This is one of the cheapest gemstone mining methods and gives good results as well.

[3] Shaft Mining

In this method, vertical tunnels are created below the mountains and through the lift miners moves up and down the mines. The vertical tunnels are called as shafts. Two shafts are created. One is used for the movement of the miners inside the shafts and the other shaft for brining the material on the ground. From the man shaft, small tunnels are made that reaches the rocks possessing the gems. These small tunnels are used for blasting and when the rocks breaks into small chunks those are brought up on the ground through the second shaft. After the work is finished the mines are closed by refilling the shafts with dirt, mud, pebbles and cement etc. This is quite a costly method.

[4] Slope Mining

Slope mining too has shafts but these shafts are first made slant and then parallel to the ground. Usually, this mining is done when it is not possible to make the straight shafts therefore it is named as slope mining. The tunnels are not very deep in the gemstone mining method. Using the conveyor the broken are rocks are brought out.

[5] Hard Rock Mining

Same as drift mining, tunnels are made inside the grounds instead of mountains. First a small opening is made which is referred as Adit. Later, using Adit, tunnels are made vertically deep down the ground using explosives like dynamite. The tunnels are called as shafts. Like wise many shafts are made and each one has a different function. For examples – one could be used for miners going inside and coming back to the ground, second for air ventilation and so on. At the end of the shaft, there one more shaft is made that leads to the rock that contains gemstones. Deep inside the earth crust many different floors are created and one floor after the other is completed. This is the most dangerous gemstone mining method and therefore is brought into practice quite less.

In all the mining methods the rocks are broken into medium or small chunks using the explosives such as dynamite. The broken rocks are then sent to the other processing plant where the gemstones are obtained in the form of raw stone. These raw stone reach to the next level of gemstone processing that involves cleaning, cutting and polishing etc. The gemstone that finally gets mounted to the awesome jewelry pieces, from the scratch passes through the numerous steps that involve the sweat of many people.

It is very easy and classy to wear the gemstone jewelry but the amount of hard work involved in obtaining these precious and semi-precious gemstones through the mining methods is immense. Gemstone mining methods are certainly mind-numbing and it is an exclusive proficiency of finding inimitable raw stones from mines that are crafted into amazing gemstone jewelry!!

Diamond Marketing by De Beers

by Erum Qureshi

That ‘a diamond is forever’ is the probably the world’s greatest, most expensive and widely circulated PR scam! The on-going, century-long campaign by diamond giant De Beers owned by the Oppenheimer family began in 1938; De Beers needed a slogan for diamonds that expressed both the theme of romance and everlasting love.

The on-going, century-long campaign by diamond giant De Beers owned by the Oppenheimer family began in 1938; De Beers needed a slogan for diamonds that expressed both the theme of romance and everlasting love.

Consequently, N.W Ayer, De Beers’ New York based ad agency, came up with the line ‘A diamond is forever’. Even though diamonds can be shattered, chipped, discolored or reduced to ash, the concept of eternity perfectly captured the magical qualities their client wanted to attribute to their product. The campaign began in America and projected the diamond onto the man-woman relationship, subtly altering the public’s view of the way a man courts, and wins a woman. That it was forever also aimed to associate the stone with a sentiment that inhibited the public from ever reselling it. Ask anyone who has tried reselling their diamonds, and they will tell you how it is practically impossible to even recover a diamond’s cost price, let alone make a profit on that investment.

De Beers controls over 60% of the world’s diamond market; it has stockpiles of the stones and sets the price on them. However, this invention was more than just a monopoly for fixing diamond prices, it was a strategy formulated for De Beers by N.W Ayer in America and later followed by J. Walter Thompson in the rest of the world for converting carbon crystals into globally accepted icons of wealth, romance and power.

The diamond ring was pitched not as a marketable product but as a symbol of everlasting love and security and an inseparable part of courtship and marital bliss. There was no direct sale to be made, no brand name to be impressed on the public, just the idea of eternal emotional value surrounding the diamond. The pitch succeeded. And how! Except for those few stones that have been destroyed, every gem quality diamond that has ever been cut and polished still exists today.

Kimberly diamond mine, owned by De Beers group

Nearly a hundred million women wear diamonds, while millions of others keep them in vaults and safe-deposit boxes as family heirlooms. The public holds an estimated 500 million carats of gem quality diamonds (more than fifty times the annual production of gem quality diamonds in any given year by De Beers). If a significant section of the public ever decided to put these diamonds up for sale in the market, the price so carefully controlled and sustained by De Beers could never be maintained. For the diamond invention to survive, for De Beers itself to survive, these hundred million women had to be stopped from ever parting with their diamonds.

It was the symbolism, not the value. The idea that diamonds are a gift of love: the larger and finer the diamond, the greater the expression of love. Men are aware of the symbolism value, which is why they have to buy a diamond ring even if they know it’s a creation of the De Beers monopoly. De Beers spent millions to ingrain in the minds of everyone that they have to shell out thousands for the diamond if a man wants to marry his woman. It was how one could make ‘two months’ salary last forever’!

De Beers sent representatives to high schools across the country to teach young girls about the value of diamonds and feed them romantic dreams. Word was spread by diamonds worn by Hollywood stars, British Royalty and wives and daughters of political leaders and celebrities, by women who could make the common man’s wife or girlfriend say ‘I wish I had what she has’. Love began to be measured in carats.

In the 1960’s diamonds were discovered in Siberia and De Beers saw its control-supply chain monopoly being threatened. It closed a secret deal with the Soviets to market these small stones and the marketing campaign for ‘eternity anniversary rings’ was launched, targeting an entirely new market of older married women.

Perhaps the biggest controversy De Beers ever faced was that of Conflict Diamonds. Although the industry has started following the Kimberly process (wherein a diamond is monitored and certified at every point of its production process), not very long ago De Beers was still buying Angolan diamonds and insisting that tracking stones was unfeasible. No ad campaign for De Beers ever highlighted the fact that mining undertaken in African countries violate innumerable human rights. In these mines, small children are made to dig in small underground pits, where men and women can’t fit, even though child labor is illegal.

Workers and communities in and around mines suffer due to state orchestrated repression, toxic run-off from unsafe mining practices, tuberculosis, HIV infections, prostitution, immune disorders, racial discrimination and slavery. In the past decade, millions of people have been dispossessed of their livelihoods, land, future and their lives in places like Katanga, Congo and Zaire where De Beers has its mining operations. Such topics are off the agenda for De Beers, the media and the women who choose to wear these diamonds. For them, it serves to 1) Reassure them that a man values them,
2) Reassures them that he is financially stable, and
3) Draws respect from other women because of Nos. 1 and 2.

The question why the people from the world’s richest mining metropolises are also one of the world’s poorest and most downtrodden does not occur to anyone.

Back home in India where 80 % of the world’s diamonds are cut, children are given the smallest stones to work on because their eyes and fingers are better suited for shaping the tiny facets. These children suffer from eyestrain, repetitive motion injuries and lacerated lungs from diamond dust. Skilled laborers in India earn less than 1/5th of what their counterparts in Europe or America do. Where is the romance in that?

Today, being faced with increased competition, the threat of synthetic diamonds and newly discovered diamond reserves, De Beers has decided to stop buying the world’s surplus diamonds as it has been doing all these decades to control supply. It markets itself as a clean diamond company, guaranteeing bloodless stones because it lies in its best commercial interests to do so. It would even suit De Beers if the supply of African diamonds somehow dried up; they could then get rid of its $4bn stockpile of accumulated carbon. As always, exploiters minimize the awareness of the resources they target, laying emphasis instead on the glamour and lure of the product they market.

Differentiating Diamond and its Imitation

by Erum Qureshi

There are various decisive tests to assess the authenticity of a diamond. The Ceres Diamond probe, Rayner Diamond Tester, Diamond Pen are a few popular instruments.

The unique hardness of diamond enables it to scratch the polished surface of synthetic corundum and no other substance on earth can do this. However, using hardness as a test is considered crude and seldom necessary since the diamond itself may suffer some damage in doing so.

The most notable diamond Simulants are synthetic cubic zirconia, synthetic strontium titanate, YAG (yttrium aluminium garnet) and GGG (gadolinium gallium garnet).

Synthetic white spinel, made from the Verneuil flame-fusion process is also used as a substitute for small diamonds in multiple gem settings; moreover, it is singly refractive. But it gives a Refractometer reading of 1.726, has a low degree of fire, and measures 8 on Moh’s scale of hardness. Synthetic rutile has six times the dispersion of diamond but is easily recognizable because of its high refractive indices and a large double refraction. YAG (yttrium Aluminium garnet) has the appearance of having properties of a diamond Simulants, and is differentiated from diamond by the Immersion Contrast method.

Danger of confusion between diamond and its simulants became much more apparent when Cubic Zirconia appeared on the market.

There was a demand for developing special apparatus that would make the distinction between diamond and its Simulants rapid and certain, even in the case of mounted stones and with a very rudimentary knowledge of gemology. The most ingenious and effective method of differentiating diamond from all other gemstones makes use of its outstanding property as a thermal conductor, which is higher than for any other substance – higher than even copper or silver.

The Ceres Diamond probe was the first to exploit this property even with small specimens and in the case of mounted stones. The Ceres probe has two thermistors and a small copper tip in a convenient holder. When the instrument is switched on, the tip of the probe warms up. When it is gently held to the surface of the stone to be tested, the needle of the instrument swings to the right and a green light flashes in case of a diamond. With any other stone, the needle of the meter swings to the left and a red light flashes. The probe of the Ceres instrument is very delicate and needs handling with care, but even very small stones can be tested with it.

Another instrument of the same kind is the British made Rayner Diamond Tester. Such equipment is very costly but to anyone dealing with diamond jewelry, this is a relatively small matter when compared with the value of the goods tested.

The GIA has made use of another property of diamond to differentiate it from simulants. This particular property is the diamond’s affinity for grease or greasy liquids. The Gemological Institute of America has produced a Diamond Pen, charged with a specially prepared liquid, which left a visible mark when drawn across the table facet of a diamond, but which broke up into droplets on the surface of all other stones.

Another test for singling out a diamond simulant is the Immersion Contrast method. When light is placed over stones (Strontium titanate, YAG, GGG and CZ) immersed in di-iodomethane (methylene iodide; a high density liquid with a refractive index of 1.742) or Refractometer contact fluid (RI 1.81) different stones show differing patterns. All except strontium titanate show a dark ring diminishing in width as their refractive index approaches near to that of the liquid. This is a definite visual indication of differentiation between diamond and its simulant.

Another diamond simulant, though very rare, is a diamond doublet. The top half (crown) of this consists of a diamond, which is cemented on to a pavilion of some other colorless stone. When such a stone is viewed obliquely through the table facet, a shadow of the edges of the facet can be seen on the underlying cement layer, revealing the fake.

Another way to differentiate between a diamond and its simulant is ultra violet radiation. Under long-wave ultra-violet light, diamonds will show a very varied degree of fluorescence. If all the ‘diamonds’ in a multi-stone setting show a similar fluorescence, they are certainly not diamonds. Under X-rays, almost all diamonds show a blue fluorescence and a brief exposure on film will show diamonds to be far more transparent to X-rays than any other stone. This technique is worth practicing as it is a decisive test.